Restrict Possible Usernames - Doubt using \g

Tell us what’s happening:
when I use /g in my regular expression it returns True… but does not pass the case

When I didnt use it passes all the test case…

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Link to the challenge:

If the regex has the global flag set, test() will advance the lastIndex of the regex. A subsequent use of test() will start the search at the substring of str specified by lastIndex ( exec() will also advance the lastIndex property). It is worth noting that the lastIndex will not reset when testing a different string.